Why Is My Check Engine Light On? Common Causes and What to Do
Why Is My Check Engine Light On? Common Causes and What to Do
The Dreaded Dashboard Light — What It Really Means
Few things make drivers more uneasy than seeing the check engine light (CEL) suddenly appear on the dashboard. It’s vague, it’s often unexpected, and it can leave you wondering whether your car is about to break down or if it's just a sensor glitch.
At
S&A General Auto Repair and Bodywork Shop in Alexandria, VA, we help hundreds of customers each year who come in asking the same question:
“Why is my check engine light on — and should I be worried?”
In this guide, we’ll break down:
- The
most common reasons your check engine light turns on
- How to tell whether it’s
urgent or minor
- What to do next (and what not to do)
- Why professional
diagnostics matter
What the Check Engine Light Is Telling You
The check engine light is part of your car’s onboard diagnostics system (OBD-II). It constantly monitors engine performance, emissions, and key components. When the system detects a fault — even something small — it triggers the light.
Your CEL may appear:
- Solid (less urgent, but should still be addressed)
- Flashing (urgent – may cause immediate damage)
If your light is flashing, this typically signals a serious engine misfire, which can damage the catalytic converter and other major systems. Do not ignore a flashing CEL.
Top 7 Reasons Your Check Engine Light Is On
1. Loose or Faulty Gas Cap
Believe it or not, one of the most common reasons for a CEL is also the easiest to fix. If your gas cap is:
- Loose
- Damaged
- Missing
…it can cause a drop in fuel pressure and trigger an evaporative emissions error.
What to do: Try tightening the cap. If the light doesn’t go away after a few drives, come see us for a quick scan.
2. Faulty Oxygen Sensor (O2 Sensor)
Your O2 sensor monitors the level of oxygen in your exhaust and helps regulate your fuel-air mixture. If it fails, your engine may:
- Burn too much fuel
- Run rough
- Fail emissions tests
This is a common failure on vehicles with 80,000+ miles.
3. Malfunctioning Catalytic Converter
The catalytic converter reduces harmful emissions. If it’s failing, you may notice:
- A sulfur or “rotten egg” smell
- Reduced fuel economy
- Trouble accelerating
Ignoring this issue can lead to expensive replacements. In Virginia, this is a common emissions-related repair that can cause inspection failure.
4. Spark Plug or Ignition Coil Issues
Your engine relies on spark plugs and coils to ignite the fuel-air mixture. When these fail, the result is:
- Misfiring
- Rough idling
- Poor fuel economy
- Possible stalling
This is one of the top causes for a flashing check engine light. If left unchecked, it can damage the engine or exhaust system.
5. Mass Airflow Sensor (MAF) Failure
The MAF sensor monitors how much air enters the engine. If it fails:
- The engine may hesitate or stall
- Your fuel economy drops
- The car may run too lean or too rich
This part is sensitive and can get dirty or fail with age.
6. Bad Exhaust Gas Recirculation (EGR) Valve
The EGR valve helps lower emissions by recirculating a portion of exhaust gases back into the combustion chamber. If clogged or malfunctioning, it can:
- Trigger the CEL
- Cause stalling
- Reduce power
This is another emissions-related repair that could cause you to fail a Virginia state inspection.
7. Transmission Issues
Sometimes, the CEL points to problems outside of the engine, such as:
- Transmission fluid problems
- Failing shift solenoids
- Torque converter issues
Transmission-related CEL codes are often accompanied by symptoms like delayed shifting, slipping, or hesitation.
Should You Keep Driving with the Check Engine Light On?
That depends on:
- Is it solid or flashing?
- Is your vehicle acting differently?
If the light is solid and your car feels fine, you’re probably safe to drive for a short time — but you still need diagnostics soon.
If the light is flashing, pull over safely and call us. Continuing to drive can cause expensive damage.
How We Diagnose CELs at S&A General Auto
What Our Process Looks Like
At S&A General Auto in Alexandria, we use advanced diagnostic scanners to:
- Retrieve
trouble codes (DTCs)
- Interpret the codes (some require deeper testing)
- Perform
live data analysis while the engine runs
- Conduct
component testing if needed
- Provide a
clear repair plan
We don’t just “read the code.” We investigate what’s causing the issue — because one code can mean several different problems depending on the vehicle.
"My check engine light came on and S&A diagnosed it the same day. They didn’t push extra work — just fixed the issue and explained it clearly."
—
Verified Google Review
Why a DIY Code Reader Isn't Enough
You can buy an OBD-II reader online or at an auto parts store — and they can be helpful. But they often don’t tell the full story.
For example, a “P0302” code might tell you there’s a misfire in cylinder 2. But is it the spark plug, coil, injector, or compression?
Only
professional testing can confirm the root cause.
FAQs – Check Engine Light
Can I reset the check engine light myself?
You can, but unless you fix the underlying issue, it’ll come right back. Some issues worsen if ignored.
Will I fail my Virginia emissions test with the CEL on?
Yes. If your check engine light is on, your vehicle
cannot pass emissions inspection until the problem is resolved.
How much does CEL diagnostics cost?
At S&A, we offer
affordable diagnostic scans. Cost depends on whether additional testing is needed. We always provide a clear estimate before repairs.
What if the light comes on and then turns off?
This could mean an intermittent issue. The system may have stored a code — we can scan for it even if the light is off.
Book Check Engine Light Diagnostics in Alexandria, VA
If your check engine light is on, don’t ignore it. Whether it’s a simple fix or a more serious issue, our team at S&A General Auto Repair and Bodywork Shop is here to help.
We’ll diagnose the issue quickly, explain your options, and get you safely back on the road.
Visit us: 612 C, S Pickett St, Alexandria, VA 22304
Call: (703) 370-5189
Email: sandaauto1@gmail.com
